Download Chapter 12 – Mathematics of Chemical Equations

Chapter 9 – Mathematics of
Chemical Equations
(Stoichiometry)
I. Fundamentals of Stoichiometry
A. Why do we balance
chemical reactions and what
do coefficients mean?
1. Unbalanced chemical
equation shows the
correct reactant/s and
correct product/s.
2. Balanced chemical
equation demonstrates
the Law of Conservation
of Mass or Matter
because the number of
atoms/ions of each
chemical substance is the
same on both sides of the
arrow.
a. Coefficients show
the number of particles
of each chemical
substance: molecules,
formula units, atoms,
or ions depending upon
the composition of the
substance.
b. Coefficents also
represent the number
of moles since moles
“count” particles.
3. Substances react in
specific ratios or
proportions based upon
the number of particles or
moles, not grams.
B.
Mole – Mole problems
1. general formula:
mole A
(starting)
x
mole B (ratio)
mole A
2. examples:
C. Mass – Mass problem
1. general formula:
mass x
given
1 mol x
molar
mass
mole ratio
unknown
given
x
molar mass
unknown
quantity of  moles of  moles of  quantity of
given
given
unknown
unknown
(g)
(mole ratio)
(g)
2. examples:
D. Mass – Volume of a gas
problems
1. general formula using
molar volume:
mass x
given
1 mol x
molar
mass
mole ratio x molar volume
unknown
unknown
given
quanity of  moles of  moles of  volume of
given
given
unknown
unknown
(mole ratio)
2. examples:
3. general formula using
gas densities
quantity of 
given
(g)
moles of 
given
moles of  quantity of  volume
unknown
unknown (gas density)
(mole ratio)
(g)
E. Volume – Volume
problems
1. Equal volumes of gases
under the same
temperature and pressure
contain equal numbers of
particles and
2. therefore moles
(Avogadro’s Hypothesis)
3. general formula:
vol (mol) A x vol B (mol)
vol A (mol)
3. examples:
II. Limiting Reactants
A. The quantity of the
product/s is determined by
the quantity of the reactant
that is in short supply
(limiting). Any “extra”
reactant is termed in
“excess.”
B. To determine the limiting
reactant, perform two massmass calculations. Whichever
reactant produces the smaller
quantity of the same product
is limiting.
C. Examples:
III. Percent Yield
A. Compares the actual
amount of product produced
in an experiment to the
theoretical amount calculated
using stoichiometry
B.
Formula:
% yield = experimental yield x 100
theoretical yield
1. Usually the
experimental amount
produced is less than the
theoretical amount as
calculated through
stoichiometry
2. example:
3. the higher the percent
yield, the more successful
or efficient the procedure
C. Actual yield (experimental
yield) versus theoretical yield
1. actual or experimental
yield is the amount of
product produced from
conducting the actual
reaction, and is always
less than the calculated
amount
2. theoretical yield is
calculated from
performing a
stoichiometric calculation
3. Actual yield can be
predicted from knowing
the percent yield and
theoretical yield
a. Examples (pg 318): see sample problem G
IV. Stoichiometric calculations
involving particles
A. To calculate particles you
must use Avogadro’s number
1. one mole of particles
(ions, molecules, atoms, or
formula units contains)
6.02 x 1023 particles.
B. Example calculations
1.
2.